The present invention relates to electronic devices, and, more particularly, to devices useful for controlling battery charging.
Battery Chargers
The widespread use of battery-powered portable computers (e.g., notebooks, laptops and palmtops) with high performance relies on efficient battery utilization. In particular, portable computers typically use rechargeable batteries (e.g., lithium, nickel-cadmium, or nickel metal hydride) which weigh just a few pounds and deliver 4 to 8 volts. Such batteries provide roughly three hours of computing time, but require about as long to be recharged. Such slow recharging is a problem and typically demands that users have several batteries with some recharging while others are being used.
Known battery chargers apply a constant voltage across a discharged battery with the applied voltage determined by the maximum voltage acceptable by the battery. FIG. 1a heuristically illustrates such a battery charger with V.sub.MAX the maximum voltage acceptable by the battery and I.sub.MAX the maximum current; the resistor R and V.sub.MAX are the adjustable parameters. FIG. 1b is the load line for the battery charger of FIG. 1a and shows charging current I as a function of the battery voltage V. As the load line shows, the charging current begins at I.sub.MAX with a totally discharged battery as indicated by point A. The battery rapidly charges and its voltage increases and the charging current decreases with the operating point moving down the load line as shown by arrow B. Then as the battery voltage rises to near V.sub.MAX, the charging current falls to zero as indicated by point C. And the small charging current implies a large charging time. Indeed, most of the charging time will be during operation approaching point C.
Furthermore, the different chemistries of various battery types preferably use differing recharging programs, and varying battery capacities (sizes) demand differing charging currents. However, known battery chargers cannot adapt to such a variety charging conditions and remain simple to use.
Features
The present invention provides battery charging with a multipart load line by sensing battery charge and responsively adjusting charging voltage and series resistance. This permits adaptation to various battery chemistries and capacities, and, in particular, allows for constant charging with an approximately constant current and for trickle charging with a trickle current. The invention further provides an integrated circuit battery charger with programmable multipart load line in a three pin package. This yields an easy-to-use battery charger which may be designed into a battery pack and programmed for near-optimal recharging. Further, the battery charger may be tested and trimmed after packaging by one-wire communication.